Pigment dispersions



memd June 26, 1945 2,379,070

PIGMENT DISPEBSION S Peter Bertles Evans, Wynnewood, and William Edwin Scott, Drexel Hill, Pa., assignors to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation oi Delaware No Drawing. Application March 14, 1941,- Serlal No. 383,344

2 Claims.

This invention relates to the dispersion of pi ments in resin solutions and more particularly to the dismrsion of pigments classified as organophilic and hydrophilic pigments as determined tilled water according to procedures described e. g. by Harkins, W. D. Jordan, H. F., J. Amer. Chem. Soc. 52,1751 (1930).

Among organophilic pigments may be noted from contact angle measurements. s toluidine red, Hansa yellow, phthalocyanine blue In the manufacture of synthetic resin enamels and pigments prepared from organic dyestuiis in e. g. fatty oil modified alkyd resin enamels a cusgeneral. Some of the organic dyestufl pigments, ternary practice is to disperse, or as more com- I however, are hydrophilio e. g. those of the metallic manly designated grind, the pigment in a portion salt type. The hydrophilic pigments include those of the resin solution ina ball or pebble mill. This vlo of an. inorganic nature usually the oxides, lead intermediate product usually designated as a mill chromates and a few of the organic dyestufi type base is then further mixed with additional resin as noted above. solution. solvents, thinners, driers etc. to produce The organophilic solvents are of the parafiin finished enamel. While thisprocedure has exhydrocarbon type, particularly those boiling below tensive commercial application difiiculty is fre- 8 C'- T e hi he boiling p n hydiflcaibon auently encountered in obtaining a satisfactorily and aromatic hydrocarbon solvents are less high gloss and good flowing properties in the finstrongly organophilic. The strongly hydrophilic ished enamel particularly when it is necessary to solvents include esters, ketones, alcohols, etc. As use a relatively high pigment to vehicle ratio in a very strongly organophiiic solvent may be noted the finished product in order to obtain adequate 2o varnish makers and painter naphtha Wlth s hiding. Since emphasis is quite often placed on gloss and flow in enamel films it is highly desirable to economically produce enamels which will yield high gloss films and thus adequately meet the demands of the trade.

of l35-190 C. is very weakly organophilic or relboiling range of loll-167 C. As a strongly organophilic solvent may be noted mineral spirits with a boiling range of 150-215" 0. whereas a high solvency petroleum naphtha having a boiling range This invention has as a principal object the proatively hydrophiiic. vision of means for preparing high gloss and good The invention will be more fully understood 3 ynthetic resin enamels from the following examples which are given by A further object is the provision of means for preparing high gloss fatty oil or oil acid modified alkyd resin enamels.

A still further object is the preparation of high gloss fatty oil or fatty oil acid modified alkyd resin enamels having a high pigment to vehicle ratio.

determined by the results of'measurements of a constant (designated as Km) characteristic of each pigment, as described e. g. by Bartell, F. E.

and Osterhof, H. J. in J. Ind. and Eng. Chem. 19, 1277 (1927) and Bartell, F. E. and Bar-tell, L. 5., J. Amer. Chem. Soc. 56, 2205 (1934). The classification of solvents (or thinners) as to their position on the organophilic hydrophilic scale may be determined by the results of measurements of the interfacial tensions of the solvents against disway 05. illustration but not by limitation except insofar as defined in the appended claims. The parts are by weight:

EXAMPLE I A. Hansa yellow mill base Qther objects will be apparent from the detailed description of the invention. Parts These objects are accomplished by dispersing Hansa yellow pigment 33.3 organophilic pigments in an organophilic solvent Alkyd resin (solids) 6.3 solution of the resin and hydrophilic pigments in High solvency petroleum naphtha 1.6 a hydrophiiic solvent solution of the resin with a Mineral spirits 3.8 high pigment to resin ratio. V. M. 82 P. naphtha 54.6

The classification of pigments as to their position on the organophilic-hydrophilic scale may be 100.0

This mill base in which the solvent was predominantly of the very strongly organophiiic t (V. M 8.: P. naphtha) was smooth in consistency, easily handled and possessed a clean color. When used in the preparation of a finished enamel it produced such an enamel having a highly satisfactory gloss and possessing other desirable and necessary'properties. It will be observed that the pigment to resin ratio. in this mill base is aD- proximately 5:1. The common practice of dispersing this pigment is according to the following composition:

The pigment to resin ratio here is 1:1.1 with a much reduced amount of the organophilic solvent. This mill base isbadiy flocculated, diflicult to remove from the mill in which it is dispersed and produces finished enamels or unsatisfactory gloss. As the amount of very strongly organophilic solvent is increased together with an increase in the pigment to resin ratio the satisfactory product of the first formulation above is produced. The small amount of the weakly organophilic solvent in the formula A is introduced with the resin solution and may be, if desired, replaced in the manufacture of the resin with the strongly organophilic solvent viz. V. M. and P. naphtha.

I The alkyd resin used in this and subsequent examples was a 52% linseed oil modified glyceryl phthalate. Other non-drying, semi-drying or drying oil or fatty oil acid modified alkyd resins may be used and such modification will be readily apparent to those skilled in the art.

Exwts 11 Fire toner mm base Parts Fire toner pigment 45.2 Alkyd resin (solids) 6.5 High solvency petroleum naphtha 1.6 Mineral spirits 3.8 V. M. 8: P. naphtha 42.9

This mill base was prepared as described under Example I. The pigment binder ratio is approximately 7:1. This mill base yields markedly improved dispersion of the pigment, improved flow and improved gloss in the enamels in which it is used over the common mill base of this pigment when dispersed in the presence of weakly organophilic (or hydrophilic) solvents. In the mill base as commonly used the pigment to vehicle ratio is approximately 1.5: l and the material leaves much to be desired with respect to gloss in films from enamels in which the mill base is used.

As previously noted the small amount of weakly organophilic solvent in the mill base is introduced through the resin solution and may be readily replaced by the strongly organophilic solvent. The use of the small amount is largely a matter of expediency since the resin solution are usually prepared with these solvents.

Exmns III Toluidine red mill base obtained which when used in finished enamels produces such having amarkedly improved and satisfactory gloss over enamels prepared from a mill base made with the weakly organophilic solvent.

Parts Toluidine red pigment 51.7 Alkyd resin (solids) 7.4 High solvency petroleum naphtha; 1.8 Mineral spiri 4.3 V. M. & P. naphtha 34.8

The pigment to resin ratio in this improved mill base is approximately 7:1, a remarkable increase over the present standard practice.

Exmn IV Rubine red toner mill base Parts Rubine red toner 58.6 Alkyd resin (solids) 9.8 High solvency petroleum naphtha 28.0 Mineral spirits 5.6

This mill base is representative of a hydrophilic pigment dispersed in the presence of a weakly organophilic or relatively hydrophillc solvent or thinner with a pigment to resin ratio of approximately 6: 1. Enamels prepared from this mill base were clean in color, free flowing and produced films of highly satisfactory gloss characteristics. As commonly prepared in the presence of a strongly organophilic solvent or thinner the pigment to resin ratio is approximately 2:1. As in the examples of the organophillc pigments the conditions for the dispersion must include both an increase in the pigment to resin ratio and the use of a proper solvent or thinner, in this example a weakly organophilic or hydrophilic solvent with the hydrophilic pigment.

ExAurLl V Chromium ozrlde mill base The mill base of this pigment is commonly'prepared in the presence of mineral spirits which is a strongly organophilic solvent, has a pigment to resin ratio of 3.9: 1, is poor in color and in general produces enamels low in gloss. Chromium oxide is prone to discoloration when dispersed or ground in a ball mill. When this pigment is dispersed in the presence of a preponderant amount of a weakly organophilic or relatively hydrophilic solvent as high solvency petroleum naphtha with increased pigment to resin ratio as, for example, according to the following formulation, a mill base of excellent color and flow is obtained. This mill base produces enamels of excellent color and gloss.

Parts Chromium oxide pigment 80.9 Alkyd resin (solids) 5.4 High solvency petroleum naphtha, 10.6 Mineral spirits 3.1

It will be noted here that the pigment to resin ratio has been increased to approximately 15:1. The small amount of mineral spirits is introduced through the resin solution and may be easily replaced by the high solvency petroleum naphtha.

LE VI Ferrite yellow mill base exemplifies such a mill base.

7 Parts Ferrite yellow pigment 68.6 Alkyd resin (solids) 6.8 High solvency petroleum naphtha 20.8 Mineral spirits 3.8

Similar results are obtained with the hydrophilic pigment red iron oxide.

While the resinous constituent of the mill in the examples is an alkyd resin other synthetic resins as the urea-formaldehyde type, phenolformaldehyde type, etc., as well as oleoresinous vehicles may be used in place thereof.

It will be apparent from the above examples that markedly improved mill bases which produce improved enamels in which they are used have been developed. It will be noted that the present invention in using strongly organophilic solvents in the dispensing medium to disperse or ganophilic pigments is contrary to present known practice. In the present state of the art where low gloss is encountered, it is customary to use so-called richer solvents (hydrophilic) in attempting to obtain better gloss rather than the so-called lean solvents (organophilic) of the low boiling aliphatic type. Furthermore the present invention embodies both a high pigment to resin ratio and the use of an organophilic solvent with an organophilic pigment and a hydrophilic solvent with a hydrophilic pigment. Neither of the conditions alone produces a satisfactory effective result.

In place of the high solvency petroleum naphtha may be used aromatic hydrocarbons in general, such as benzene, toluene, xylene, etc.

and in certain instances alcohols, esters, or

centimeter; as hydrophilic or weakly orgelnophilic solvents or thinners, those having an interfacial tension against distilled water of 35 dynes per centimeter or less.

The choice of the particular solvent or solvents will depend on varying conditions and may be made with discretion so long as it meets the requirements of the classification as an organophilic or hydrophilic solvent.

The present invention presents as principal advantages improved gloss in films prepared from enamels in which the mill bases are used; marked reduction or practical elimination of discoloration of the pigment during the dispersion due to the higher dispersion consistencies possible with consequent reduction in abrasion of the steel balls; and reduction in manufacturing costs which result from increased pigment concentration of the mill base without any increase in the time of dispersion, commonly termed grinding cycles. Further, a higher degree of dispersion and markedly improved flow is obtained which is subsequently evidenced in the improved quality of the enamels. Other advantages will be readily apparent to those skilled in the art.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore, it is not intended to be limited except as indicated in the appended claims.

We claim:

l. A mill base for preparing a coating composition which yields a high gloss on drying containing in proportion from 5 to 15 parts of pigment and 1 part of a resin as the sole film-forming agent, and in addition thereto a solvent, the said pigment being organophilic and consisting essentially of a non-metallic organic dye, the said solvent being strongly organophilic consisting essentially of paraflln hydrocarbons boiling below 215 C. and having an interfacial tension as against p ure water greater than 35 dynes per centimeter.

2. In the process of preparing coating compositions which yield a high gloss on drying from a mill base which containsjrom 5 to 15 parts of pigment to each part of resin and the resin is the sole film-forming agent, the improvement which comprises dispersing an organophilic pigment consisting essentially of a non-metallic organic dye in a vehicle containing the resin and a strongly organophilicsolvent consisting essentially of paraffin hydrocarbons boiling below 215 C. and having an interfacial tension as against pure water greater than 35 dynes per centimeter.

PETER B. EVANS. WILLIAM E. SCO'I'I'. 

